Sail for a wind-powered vehicle

ABSTRACT

A sail for a wind powered vehicle such as a surfboard, sailing boat or the like is provided wherein a sail is connected along its front edge to a mast and wherein the said sail at its clew or at its lower edge is connected to a boom. The boom is connected in a hinged manner to the mast. At the free rear edge of the sail, at least one sail part is provided which is adjustable in the sail plane so that the overall area of the sail can be decreased or increased.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sail for a wind-powered vehicle suchas surfboard, sailing boat or the like.

Sails for vehicles of the kind mentioned above are widely known andthere are several embodiments regarding their size and form. Accordingto the wind situation although with a single vehicle a sail of anadapted size may be used in order to reach a high velocity at the onehand, and to diminish the danger of capsizing as far as possible. It isusual for sailing boats to reef the sailing area of the sail whenrequired, i.e. to move the total sail downwards in relation to the mast,and to roll or fold the lower area of the sail. It is usual for sails ofsurfboards to use several differently sized sails for a single surfboardwhich are used according to the wind situation. A change of the sailarea during the usage, however, is difficult and impractical.

A surfing sail is known from WO 91/11361 comprising a base sail which atits front edge is connected to a mast which in a usual manner can beconnected to a bifurcate boom, and at its clew is connected to the otherend of the bifurcate boom, and an additional sail serving for thereefing operation. The additional sail has a triangle shape and is cutnarrow and high, and is pivotally connected at its head in the upperarea of the base sail adjacent to the rear edge thereof, and in thelower area approximately at the level of the bifurcate boom is providedwith a guiding web which is arranged and bent such that it is pivoted ata circular path when pivoting the additional sail with the circular pathin the radius thereof corresponding with the distance of the guiding webfrom the fastening point where the additional sail is secured at thebase sail. The guiding web is displaceable in the length thereof suchthat the additional sail may be pivoted inwards and outwards during thesurfing.

With this surfing sail, the sail area is variable, however, there is thegreat disadvantage in practical operation that when varying the sailarea this is accomplished for practical reasons only in the lower areashortly above the bifurcate boom. Thereby, at each variation of the sailarea the center of area and thereby the pressure point of the sail isdisplaced upwards which results in a more difficult handling of the sailby the surfing person. A further disadvantage is that, close to the peakof the sail, a pivoting joint is required which in this area of the sailrequires a corresponding rigidity which may be only attained bydesigning the mast in the peak thereof relatively rigid. Furthermoreapplications, in this case the pivoting joint in the peak area of themast have a very negative influence on the weight distribution. Thehandling of the sail is better if the mast and sail are lighter in thetop area thereof. Because of the lever forces which are caused byrelatively large mast lengths modern sails in particular surfing sailsand masts are made especially light in the top area. During the lastyears almost exclusively modern masts are used which comprise a socalled flex dynamic, i.e. a strongly flexible mast top which yields whenthe wind pressure raises suddenly, and which thereby automaticallydecreases the sail area exposed to the wind for a while. This flexdynamic in modern sails is additionally supported by a sail top which isstiffened by sail laths and which comprises a twist dynamic whichcorresponding with the flex dynamic of the mast deforms the sail toparea when the flexible mast top yields, and thereby decreases the sailarea without the sailor or surfer having to operate it himself. The useof a mast with flex dynamic, and also the use of a sail with twistdynamic are not possible with the sails known from WO 91/11361 becauseof the construction.

Furthermore a surfing sail is known from GB 2 235 671 A wherein anadjustable sail part may be displaced upwards and downwards in parallelwith the mast. The displacement of the adjustable sail part is attainedby cable control with at least one of the cables guided over the top ofthe mast, and a deflection roller positioned there for pulling theadjustable sail part upwards, and in parallel with the mast, andsecuring it there by this cable control when the maximal area of thesail is required. For receiving the resulting forces with the deflectionroller at the mast top the mast has to have a large stability andrigidity up to its top which results therein that with this known surfsail no mast with a flex dynamic in its upper area may be used. Ifsomebody uses this known sail at a modern mast with a flex dynamic thedisadvantage would result that the mast top with the full area of sailswould be too soft, and with a small area of sails would be too hardconsidering the twist dynamics explained above. A change of the frontedge length cannot be transferred to modern sails with a twist dynamic.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a generic sailwherein in a simple fashion a variation of the sail area is possiblewithout having a negative influence on the sail characteristic, andwhich is suitable for a use with modern flex dynamic masts with aflexible upper mast end area without any restrictions. Therein the sailis to be used with sailing boats and catamarans as well as withsurfboards and other wind-powered vehicles.

According to the invention the object is attained with a generic sailcharacterized in that the adjustable sail part can be displacedsubstantially perpendicular to the free rear edge of the sail and/orsubstantially parallel to the boom.

Specifically, the sail of the present invention can be connected alongits front edge to a mast wherein the sail at its clew or at or near itslower edge can be connected to a boom which is connected in a hingedmanner to the mast. In the region of its free rear edge, the sailcomprises at least one sail part which is adjustable in the sail planeby moving the sail part laterally in its adjusting direction. As aresult, the total surface area of the sail can be decreased by movingthe sail part towards the mast or the total area of the sail can beincreased by moving the sail part away from the mast.

According to the invention it is advantageously provided to decrease orincrease the sail in a simple fashion and even during the use of theassociated vehicle in order to adapt the sail area to the windconditions met. As only a displacement of the displaceable sail part isrequired for varying the sail area the handling is very simple whichmakes the new sail usable in particular for surfboards. As thedisplacing direction of the adjustable sail part substantially extendsperpendicular to the free edge of the sail, or in parallel with theboom, respectively, which is substantially in horizontal direction thelargest relative area variation of the sail may be attained withrelatively small displacement distances. According to the inventionadvantageously the length of the front edge of the sail remainsunchanged such that without any problems a flex dynamic mast, e.g. ofcarbon material may be used wherein the flex dynamic thereof isunchanged by the embodiment of the sail with an adjustable size.Furthermore the sail area, when adjusting the adjustable sail part, ischanged only at the level of the bifurcate boom but for practicalreasons is uniformly decreased or increased across the total altitude ofthe sail and the pressure point of the sail is only slightly displacedbackwards or forwards in horizontal direction but in no case upwards ordownwards such that the sail characteristic is almost unchanged which isimportant for handling the sail. Simultaneously, the sail top arearemains unchanged which is so important for the flex dynamic and twistdynamic. A sail wherein the pressure point would be displaced upwardswhen increasing the sail area would require larger holding forces whencompared with a sail with a lower sail pressure point which is verydisadvantageous in particular in critical situations e.g. when turningthe boat or in gust winds because the sail would not perform in a waythe sailor or surfer is used to. This disadvantage is completely avoidedwith the sail according to the invention.

Furthermore it is proposed that in the sail several guiding profiles arearranged in parallel with each other, extending in the displacingdirection, and simultaneously serving as sail laths, and that in theguiding profiles several displacing webs are guided which are connectedto the displaceable sail part. By this construction it is attained thatthe displaceable sail part at the one hand may be displaced with smalleffort, and that at the other hand the sail in total and thedisplaceable sail part in particular are sufficiently form stable assuch and perform as an integral sail when used.

In order not to limit the size of the adjustable sail part to an areaabove the boom, in particular with a surfing sail, and in order to usethe boom for the displacement of the adjustable sail part is proposedthat the boom substantially extends in parallel with the guidingprofile, and is designed variable in length in its end area facing awayfrom the mast. Bifurcated booms which are variable in length are knownespecially for surfboard sails, however, only in connection with severalsails, each with a firm sail area.

Furthermore it is proposed that in the upper end area of the sail atleast one sail lath with a firm length is provided, and that theadjustable sail part extends upwards to the first guiding profile ascounted from upwards down. In this way the upper end area of the sail isnot dependent from the position of the adjustable sail part in sizethereof. This results in the advantage that when using a mast with flexdynamic, i.e. with an especially flexible upper end area the cooperationof the upper sail area with twist dynamic and the flexible mast end isnot impaired. Thereby the sail will react independent from the presentposition of the adjustable sail part when the wind suddenly freshes-upin a way which is used to the sailor or surfer such that the handling ofthe sail is not impaired.

In an embodiment, the present invention provides a sail assembly forattachment to a mast. The sail assembly comprises a sail comprising afront edge, a rear edge and a clew. The front edge of the sail isconnected to the mast. The clew is connected to a boom. The boom ishingedly connected to the mast. The sail defines a sail plane having atotal area. The rear edge of the sail comprises at least one adjustablesail part which is adjustable in the sail plane by way of adjusting thelongitudinal position of the adjustable sail part in a first adjustingdirection substantially parallel to the boom lath and towards the mastwherein the area of the sail plane is decreased and by adjusting thelateral position of the adjustable sail part in a second adjustingdirection substantially parallel to the boom and away from the mastwherein the area of the sail plane is increased.

In an embodiment, the sail comprises a plurality of guiding profilesdisposed parallel to each other and the boom and extending along thesail in the adjusting direction. The adjustable sail part comprising aplurality of displacing webs disposed parallel to each other and theboom and extending along the adjustable sail part in the adjustingdirections. The guiding profiles serving as sail laths. Each guidingprofile accommodating at least one displacing web.

In an embodiment, the boom comprises an extendable rear end forincreasing the length of the boom along the second adjusting direction.

In an embodiment, the sail further comprises an upper end area. Theupper end area of the sail comprises at least one sail lath. Theplurality of guiding profiles further comprising an uppermost guidingprofile disposed below the sail lath of the upper end area and below theupper end area. The adjustable sail part extending upwards to theuppermost guiding profile.

In an embodiment, each guiding profile accommodates two displacing webs.Each guiding profile comprises a cross beam disposed between twoopposing end sections. The cross beam is disposed generallyperpendicular to the sail plane and to the end sections. The endsections are bent towards each other and from two profiled longitudinalslots with a cross beam disposed therebetween. Each profiledlongitudinal slot accommodates one of the displacing webs of theadjustable sail part.

In an embodiment, the adjustable sail part comprises a rear edge and thedisplacing webs of the adjustable sail part are arranged in pairs. Eachpair of displacing webs is accommodated in one of the guiding profileson opposing sides of the cross beam. Each pair of displacing webs isconnected to one another at the rear edge of the adjustable sail part.

In an embodiment, the guiding profiles comprise a T-shaped cross sectionwith a cross beam that extends perpendicular to the sail plane and whichis disposed between the sail and an end section that extends parallel tothe sail plane. The displacing webs comprise a C-shaped cross sectionand the end section of each guiding profile is slidably captured in oneof the C-shaped cross sections of one of the displacing webs.

In an embodiment, the sail comprises two plies and forms a pocketbetween the two plies. The adjustable sail part is extendable in thefirst adjusting direction where the adjustable sail part is pushed intothe pocket and in the second adjusting direction where the adjustablesail part is retracted from the pocket.

In an embodiment, the guiding profiles and displacing webs arefabricated from plastic. The sail and the adjustable sail part are heatbonded or welded to the guiding profiles and displacing websrespectively.

In an embodiment, the adjustable sail part may be locked into an inwardposition and into an outward position by a releasable locking mechanism.

In an embodiment, the releasable locking mechanism comprises snap-inelements attached to the guiding profiles and displacing webs.

In an embodiment, the guiding profiles comprise rear ends. Thereleasable locking mechanism comprises manually adjustable clampingelements which are attached to the rear ends of the guiding profiles.

In an embodiment, the sail comprises two plies, folded front edge, tworear edges (one for each ply) and a clew. The sail defines a pocketbetween the two plies. The front edge of the sail is connected to themast. The clew of the sail is connected to the boom. The boom isbifurcated or, includes two rearwardly extending legs, an extends alongeach ply of the sail. The sail defines a sail plane having a total area.The rear edges of the sail are connected to at least one adjustable sailpart which is adjustable in the sail plane in one of two directions byadjusting the longitudinal position of the sail part in a firstadjusting direction substantially parallel to the boom and towards themast wherein the adjustable sail part moves into the pocket defined bythe two plies of the sail in the area of the sail is decreased and, byadjusting the lateral position of the adjustable sail part in a secondadjusting direction substantially parallel to the boom and away from themast wherein the adjustable sail part is retracted from the pocket andthe area of the sail plane is increased.

In an embodiment, the plies of the sail are connected by a plurality ofguiding profiles disposed parallel to each other and the boom and whichextend along the plies of the sail in the adjusting direction. Theadjustable sail part comprises a plurality of displacing webs disposedparallel to each other and the boom and extend along the adjustable sailpart. The guiding profiles serving as sail laths; each displacing webbeing accommodated in one guiding profile of each ply thereby connectingthe two plies together.

Other objects and advantages of the present invention will becomeapparent upon reading the following detailed description and appendedclaims, and upon reference to the accompanying drawings.

Preferred embodiments of the guiding profile and the displacing websguided therein are stated in the claims 5, 6 and 7. The embodimentsdescribed there at the one hand provide a low weight of the guidingprofiles and displacing webs, and at the other hand a high stability.

In order to exclude that between the stationary parts of the sail andthe adjustable sail part slots are formed which let the wind pass withthe slots decreasing the effect of the sail as far as the propulsion ofthe vehicle is concerned it is provided that the sail at least in anarea wherein the displaceable sail part is positioned with minimal sailarea is designed double ply in form of a pocket wherein the displaceablesail part may be pushed into this pocket, and retracted from thispocket.

To attain a weight of the sail as low as possible, and forsimultaneously guaranteeing high stability and rigidity it is proposedthat the guiding profiles and the displacing webs are manufactured ofplastic material, and that the sail cloth of the stationary part of thesail is connected with the guiding profiles, and the sail cloth of thedisplaceable part of the sail is connected with the displacing webs,preferably bonded or welded.

To enable the adjustment of the displaceable sail part with as littleeffort as possible, and simultaneously to exclude a non-requireddisplacement of the displaceable sail part it is provided that thedisplaceable sail part at least in its two end positions in relation tothe remaining sail is to be secured by means of releasable lockingmeans.

The locking means mentioned above e.g. may be cooperating snap-inelements at the guiding profiles and displacing webs, and eventually atthe parts of the boom displaceable in longitudinal direction towardseach other, or alternately may be manually adjustable clamping orlocking elements which are arranged at the guiding profiles preferablyat the ends facing the free edge of the sail, and eventually at thedisplaceable parts of the boom to be displaced in relation to each otherin longitudinal direction.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention in the following are explained referring toa drawing, wherein:

FIG. 1 is a plan view of a sail with a displaceable sail part made inaccordance with the present invention;

FIG. 2 is a partial enlarged view of the sail shown in FIG. 1;

FIG. 3 is a further partial enlarged view of the sail shown in FIG. 1;

FIG. 4 is a sectional view taken substantially along line IV—IV of FIG.2; and

FIG. 5 is a cross sectional view of an alternative embodiment.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The sail 1 illustrated in in FIG. 1 in the present embodiment isdesigned as a sail for a surfboard. With the front edge 11 pointing tothe left in the Figure the sail 1 is connected to a mast 3 in a commonfashion with the mast in its lower end not visible here articulatedlyconnected with an associated surfboard. Furthermore the sail 1 comprisesa bifurcate boom 30 as it is usual for surfboard sails.

In contrast to common sails, the illustrated sail 1 comprises a sailpart 20 which is displaceable in relation to a stationary sail part 10.In the FIG. 1 the displaceable sail part 20 is illustrated in itsexposed position wherein the sail 1 comprises its maximal sail area.

In the position illustrated in FIG. 1, the displaceable sail part 20 maybe pushed towards the mast 3 i.e. to the left in FIG. 1. Hereby the freeedge 22 of the sail 1 facing away from the mast 3 is displaced to theleft. When the displaceable sail part 20 has been pushed in as far aspossible the edge 22′, it forms the free edge of the sail 1 facing awayfrom the mast 3. In this way the sail area of the sail 1 may beincreased or decreased as required in order to adapt it to the windconditions met. In this way the sail 1 may replace two or more commonsails with a fixed sail area.

In order to enable the required displacement of the displaceable sailpart 20, the sail 1 is provided with several guiding profiles 14 whichsimultaneously serve as sail laths and which extend in parallel witheach other substantially perpendicular to the free edge 22 of the sail1, and in parallel with the bifurcate boom 30. The guiding profiles 14each are positioned with the one end (left in the Figure) at the mast 3,and with their other end, with the exception of the lower profile 14,reach to the free edge 22′ of the sail 1. Therein the firm sail part 10is secured with the guiding profiles 14, e.g. bonded or welded.

The displaceable sail part 20 comprises a pair of displacing webs 24 foreach guiding profile 14 with the displacing webs being aligned with theguiding profiles 14 and guided in an axially displaceable fashion in theguiding profiles. The displacing webs 24 of each pair of displacing websare connected with each other at their outer ends 24′ which face thefree edge 22. The displaceable sail part 20 as such is connected withthe displacing webs 24, e.g. bonded or welded. The bifurcate boom 30 isalso variable in length in its end area 32 facing away from the mast,and it is telescopic.

The fixed sail part 10 is made double ply in form of a pocket 13 in thearea in FIG. 1 which is hatched in thin lines. This pocket 13 is opentowards the free edge 22′, and the displaceable sail part 22 20may bepushed into this pocket 13, and retracted out of this pocket 13. Windopen slots between the fixed sail part 10 and the displaceable sail part20 thereby are avoided to the utmost degree such that the sail 1 whenused performs like an integrated sail independent from the presentposition of the displaceable sail part 20.

As it is illustrated in FIG. 1 the displaceable sail part 20 in theillustrated embodiment of the sail 1 extends across a part of the sail 1above and below the bifurcate boom 30.

In its upper area, i.e. the top of the seal 10 is provided with a sailpart of unchangeable size wherein this upper sail part is stiffened by afixed sail lath 114 which is not variable in length. The mast 3 in itsupper end area 3′ comprises an enlarged flexibility, i.e. a so calledflex dynamic. The sail 1 in its upper sail area is provided with a socalled twist dynamic corresponding to the flex dynamic of the upper mastarea 3′, with the twist dynamic offering an automatic reduction of thesail area at sudden gust force winds wherein the mast end area 3′ isflexibly bent thereby reducing also the upper sail area beyond the upperguiding profile 14. This flex dynamic of the mast end area 3′, and thetwist dynamic of the upper sail area are advantageously not influencedby the adjustable sail part 20.

As an alternative the sail 1 may be designed such that the displaceablesail part 20 extends only across the sail area above the bifurcate boom30. As a further alternative the sail 1 may comprise two separatedisplaceable sail parts 20, wherein preferably the one displaceable sailpart is positioned above the bifurcate boom 30, and the seconddisplaceable sail part is positioned below the bifurcate boom 30. In thealternate embodiments there is a stationary position of the connectionof the end of the bifurcate boom 30 facing away from the mast with thefree edge clew 12or the clew of the sail 1, respectively, so that abifurcate boom 30 with a firm length may be used. In all embodiments ofthe sail 1 relatively large variations of the sail area are enabled withsmall displacing distances such that with the sail 1 at least two oreven more common sails with a firm sail area may be replaced.

For setting the displaceable sail part 20 in required displacingpositions, at the guiding profiles 14 at the end facing the free edge22′, releasable locking means 15 are provided which prevent anon-required movement of the displacing webs 24 within the guidingprofile 14. In case an adjustment of the displaceable sail part 20 isrequired, the locking means 15 are released or loosened for a while, andafter the adjustment of the displaceable sail part 20 brought back totheir locking position. Also the bifurcate boom 30 in the presentexample comprises such locking means 15.

As it is obvious from FIG. 1, the free edge 22 of the displaceable sailpart 20 when pulled out is stiffened by the displacing webs 24 servinghere as sailing laths. Furthermore when the displaceable sail part 20 iscompletely pushed in there is a uniform extension of the free edge 1222of the firm sail part 10 such that inefficient edge areas tending toflap are avoided independent from the present position of thedisplaceable sail part 20.

FIG. 2 of the drawing illustrates in an enlarged scale a section of thedisplaceable sail part 20 together with a section of the firm sail part10. Corresponding with the double arrow in the displaceable sail part20, the sail part 20 may be displaced to the left or to the rightwherein in FIG. 2 the maximal pulled out position of the displaceablesale part 20 is illustrated. By displacing the displaceable sail part 20towards the left the latter is increasingly pushed into the firm sailpart 10 which in this area is designed as a pocket 13 wherein theguiding of the two sail parts 10, 20 relative to each other is attainedby the guiding profiles 14 and the displacing webs 24 guided therein. Atthe directly adjacent free end 24′ the displacing webs 24 are connectedwith each other to guarantee a sufficient connection of the displaceablesail part 20.

This embodiment of the displacing webs 24 with the connected free ends24′ again is illustrated in FIG. 3 in an enlarged scale.

FIG. 4 of the drawing illustrates in a cross-section along the lineIV—IV a possible embodiment of the guiding profile 14 and the displacingwebs 24. In contrast to FIG. 2, in FIG. 4, the displaceable sail part 20has been pushed into the pocket 13 of the firm sail part 10 such that inFIG. 4 also the displaceable sail part 20 is visible.

As it is obvious in the drawing the illustrated guiding profile 14 inprinciple comprises the form of a double T with the cross beam 30disposed between end sections 31 which are bent towards each other,however, leaving a longitudinal slot 14″ free between their ends. Inthis way two parallel guiding passages 14′ are formed wherein each adisplacing web 24 is guided. The displacing webs 24 in the form of theircross-sections are adapted to the cross-section of the guiding passages14′, and are made smaller than specified to enable an easy displacement.

The two plies of the firm sail part are connected, preferably bonded orwelded with the outer side of the T-cross beam of the guiding profile14. The displacement sail part 20 in the interior of the pocket 13 isconnected with the displacing webs 24 wherein the edge of the sail part20 facing the displacing web 24 is positioned inside the displacing web24 and secured there wherein preferably a bonding or welding is applied.

The guiding profile 14 as well as the displacing webs 24 preferablyconsist of plastic material to attain a light weight, a high stability,and a certain flexibility.

Finally FIG. 5 illustrates in the same way as FIG. 4 a changedembodiment of the guiding profile 14 and the associated displacing webs24. At the left and right side in FIG. 5 two sections of the firm sailpart 10 are visible extending in vertical direction wherein the firmsail part 10 is made double ply for forming the pocket 13 which has beendescribed referring to FIG. 1 and 2. A guiding profile 14 is connectedwith each sail part 10 with the guiding profile 14 having a substantialT-shaped cross-section wherein in the present embodiment also the baseof the T is enlarged to guarantee an enlarged connection area with thesail part 10. In symmetric arrangement an identical guiding profile 14is arranged at the sail part 10 being right in FIG. 5 such that theT-cross beams of the two guiding profiles 14 are directed to each otherand extend in parallel with each other. Similar to the embodiment shownin FIG. 5, the T-cross beam comprises a cross beam 32 disposed between asail ply 10 and an end section 33 which is captured in the C-shapedcross section 34 of the displacing web 24. The displacing webs 24 aredisposed on opposing surfaces of the adjustable sail part 20 and theguiding profiles 14 are disposed on the inside surfaces of the sailplies 10 so that the arrangement shown in FIG. 5 effectively attachesthe sail plies 10 together like the arrangement shown in FIG. 4.

In the middle between the two sail parts 10 there is the displaceablesail part 20 with only a section of it being visible. At both sides ofthe adjustable sail part 20 a displacing web 24 with a C-shapedcross-section is arranged wherein the two displacing webs 24 arepositioned back to back. The two displacing webs 24 receive thedisplaceable sail part 20 between them, and are connected with eachother thereby.

Each C-shaped displacing webs 24 grips around one of the T-cross beamsof the guiding profile 14 and leaves sufficient clearance for movement.In this way the displacing webs 24 with the adjustable seal part 20fastened thereto are displaceable in axial direction of the guidingprofile 14 relative to the guiding profile. A relative movement in crossdirection to the displacing direction is prevented by the form of theguiding profile 14 and the displacing web 24.

From the above description, it is apparent that the object of thepresent invention have been achieved. While only certain embodimentshave been set forth, alternative embodiments and various modificationswill be apparent from the above description to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. A sail assembly comprising: a mast, a sailcomprising a front edge, a rear edge and a clew, the front edge of thesail being connected to the mast, the clew of the sail being connectedto a boom, the boom being connected to the mast, the sail defining asail plane having an area, the rear edge of the sail comprising at leastone adjustable sail part which is adjustable in the sail plane of thesail by adjusting the longitudinal lateral position of the adjustablesail part in a first adjusting direction substantially parallel to theboom and towards the mast wherein the area of the sail plane isdecreased and by adjusting the longitudinal lateral position of theadjustable sail part in a second adjusting direction substantiallyparallel to the boom and away from the mast wherein the area of the sailplane is increased, the sail further comprising a plurality of guidingprofiles disposed parallel to each other and the boom and extendingalong the sail in the adjusting directions, the adjustable sail partcomprising a plurality of displacing webs disposed parallel to eachother and the boom and extending along the adjustable sail part in theadjusting directions, the guiding profiles serving as sail laths eachguiding profile accommodating at least one displacing web.
 2. The sailassembly of claim 1 wherein the boom comprises an extendable rear endfor increasing a length of the boom along the second adjustingdirection.
 3. The sail assembly of claim 1 wherein the sail furthercomprises an upper end area, the upper end area of the sail comprisingat least one sail lath, the plurality of guiding profiles furthercomprising an uppermost guiding profile disposed below the sail lath ofthe upper end area and below the upper end area, the adjustable sailpart extending upwards to the uppermost guiding profile.
 4. The sailassembly of claim 1 wherein each guiding profile accommodates twodisplacing webs, each guiding profile comprises cross beam disposedbetween two opposing end sections, the cross beam being disposedgenerally perpendicular to the sail plane and to the end sections, theend sections being bent towards each other and forming two profiledlongitudinal slots with the cross beam disposed therebetween, eachprofiled longitudinal slot accommodating one of the displacing webs ofthe adjustable sail part.
 5. The sail assembly of claim 4 wherein theadjustable sail part comprises a rear edge, and the displacing webs ofthe adjustable sail part are arranged in pairs, each pair of displacingwebs being accommodated in one of the guiding profiles on opposing sidesof the cross beam, each pair of displacing webs being connected to oneanother at the rear edge of the adjustable sail part.
 6. The sailassembly of claim 1 wherein the guiding profiles comprise a T-shapedcross section with a cross beam that extends perpendicular to the sailplane, the cross beam of each guiding profile being disposed between thesail and an end section that extends parallel to the sail plane, and thedisplacing webs comprising a C-shaped cross-section, the end section ofeach guiding profile being slidably captured in one of the C-shapedcross sections of one of the displacing webs.
 7. The sail assembly ofclaim 1 wherein the sail comprises two plies and forms a pocket, theadjustable sail part being extendable in the first adjusting directionwhere the adjustable sail part is pushed into the pocket and in thesecond adjusting direction where the adjustable sail part is retractedfrom the pocket.
 8. The sail assembly of claim 1 wherein the guidingprofiles and the displacing webs are fabricated from plastic, whereinthe sail and the adjustable sail part are bonded or welded to theguiding profiles and displacing webs respectively.
 9. The sail assemblyof claim 1 wherein the adjustable sail part may be locked into an inwardposition and an outward position by a releasable locking mechanism. 10.The sail assembly of claim 9 wherein the releasable locking mechanismcomprises cooperating snap-in elements attached to the guiding profilesand the displacing webs.
 11. The sail assembly of claim 9 wherein theguiding profiles comprise rear ends, the releasable locking mechanismcomprises manually adjustable clamping elements which are attached tothe rear ends of the guiding profiles.
 12. A sail assembly comprising: amast, a sail comprising two plies, a folded front edge, two rear edgesand a clew, the sail defining a pocket between the two plies, the frontedge of the sail being connected to the mast, the clew of the sail beingconnected to a boom, the boom being bifurcated and extending along eachply of the sail, the boom being connected to the mast, the sail defininga sail plane having a total area, the rear edges of the sail beingconnected to at least one adjustable sail part which is adjustable inthe sail plane of the sail by adjusting the longitudinal lateralposition of the adjustable sail part in a first adjusting directionsubstantially parallel to the boom and towards the mast wherein theadjustable sail part moves into the pocket defined by the sail and thearea of the sail plane is decreased, and by adjusting the longitudinallateral position of the adjustable sail part in a second adjustingdirection substantially parallel to the boom and away from the mastwherein the adjustable sail part is retracted from the pocket and thearea of the sail plane is increased, the plies of the sail furthercomprising a plurality of guiding profiles disposed parallel to eachother and the boom and which extend along inside surfaces of the pliesof the sail, the adjustable sail part comprising a plurality ofdisplacing webs disposed parallel to each other and on opposing surfacesof the adjustable sail part and parallel to the boom, the guidingprofiles serving as sail laths, each displacing web being accommodatedin one guiding profile of each ply.
 13. The sail assembly of claim 12wherein the boom comprises at least one extendable rear end forincreasing a length of the boom along the second adjusting direction.14. The sail assembly of claim 12 wherein the sail further comprises anupper end area, the upper end area of the sail comprising at least onesail lath, the plurality of guiding profiles further comprising twouppermost guiding profiles, one uppermost guiding profile disposed oneach ply, both of the uppermost guiding profiles being disposed belowthe sail lath of the upper end area and below the upper end area, theadjustable sail part extending upwards to the uppermost guiding profilesbut below the sail lath of the upper end area.
 15. The sail assembly ofclaim 12 wherein each guiding profile accommodates two displacing webs,each guiding profile comprises cross beam disposed between two opposingend sections, the cross beam being disposed generally perpendicular tothe sail plane and to the end sections, the end sections being benttowards each other and forming two profiled longitudinal slots with thecross beam disposed therebetween, each profiled longitudinal slotaccommodating one of the displacing webs of the adjustable sail part.16. The sail assembly of claim 15 wherein the adjustable sail partcomprises a rear edge, and the displacing webs of the adjustable sailpart are arranged in pairs, each pair of displacing webs beingaccommodated in one of the guiding profiles on opposing sides of thecross beam, each pair of displacing webs being connected to one anotherat the rear edge of the adjustable sail part.
 17. The sail assembly ofclaim 12 wherein the guiding profiles comprise a T-shaped cross sectionwith a cross beam that extends perpendicular to the sail plane, thecross beam of each guiding profile being disposed between one of thesail plies and an end section that extends parallel to the sail plane,and the displacing webs comprising two opposing C-shaped cross sections,the end section of each guiding profile being slidably captured in oneof the C-shaped cross sections of one of the displacing webs.
 18. Thesail assembly of claim 12 wherein the adjustable sail part may be lockedinto an inward position and an outward position by a releasable lockingmechanism.
 19. A sail assembly, comprising: a mast, a sail comprising afront edge, a rear edge and a clew, the front edge of the sail beingconnected to the mast, the clew of the sail being connected to a boom,the boom being connected to the mast, the sail defining a sail planehaving an area, the rear edge of the sail comprising at least oneadjustable sail part which is adjustable in the sail plane of the sailby adjusting the lateral position of the adjustable sail part in a firstadjusting direction towards the mast wherein the area of the sail planeis decreased and by adjusting the lateral position of the adjustablesail part in a second adjusting direction away from the mast wherein thearea of the sail plane is increased, the sail further comprising aplurality of guiding profiles disposed parallel to each other andextending along the sail in the adjusting directions, the adjustablesail part comprising a plurality of displacing webs disposed parallel toeach other and extending along the adjustable sail part in the adjustingdirections, the displacing webs each being aligned with a guidingprofile and guided in an axially displaceable fashion in the guidingprofiles, the guiding profiles serving as sail laths wherein eachguiding profile accommodates at least one displacing web.
 20. The sailassembly of claim 19, wherein the boom comprises an extendable rear endfor increasing a length of the boom along the second adjustingdirection.
 21. The sail assembly of claim 19, wherein the sail furthercomprises an upper end area, the upper end area of the sail comprisingat least one sail lath, the plurality of guiding profiles furthercomprising an uppermost guiding profile disposed below the sail lath ofthe upper end area and below the upper end area, the adjustable sailpart extending upwards to the uppermost guiding profile.
 22. Theassembly of claim 19, wherein each guiding profile accommodates twodisplacing webs, each guiding profile comprises a cross beam disposedbetween two opposing end sections, the cross beam being disposedgenerally perpendicular to the sail plane and to the end sections, theend sections being bent towards each other and forming two profiledlongitudinal slots with the cross beam disposed therebetween, eachprofiled longitudinal slot accommodating one of the displacing webs ofthe adjustable sail part.
 23. The sail assembly of claim 22, wherein theadjustable sail part comprises a rear edge, and the displacing webs ofthe adjustable sail part are arranged in pairs, each pair of displacingwebs being accommodated in one of the guiding profiles on opposing sidesof the cross beam, each pair of displacing webs being connected to oneanother at the rear edge of the adjustable sail part.
 24. The sailassembly of claim 19, wherein the guiding profiles comprise a T-shapedcross section with a cross beam that extends perpendicular to the sailplane, the cross beam of each guiding profile being disposed between thesail and an end section that extends parallel to the sail plane, and thedisplacing webs comprising a C-shaped cross section, the end section ofeach guiding profile being slidably captured in one of the C-shapedcross sections of one of the displacing webs.
 25. The sail assembly ofclaim 19, wherein the sail comprises two plies and forms a pocket, theadjustable sail part being extendable in the first adjusting directionwhere the adjustable sail part is pushed into the pocket and in thesecond adjusting direction where the adjustable sail part is retractedfrom the pocket.
 26. The sail assembly of claim 19, wherein the guidingprofiles and the displacing webs are fabricated from plastic, whereinthe sail and the adjustable sail part are bonded or welded to theguiding profiles and displacing webs respectively.
 27. The sail assemblyof claim 19, wherein the adjustable sail part may be locked into aninward position and an outward position by a releasable lockingmechanism.
 28. The sail assembly of claim 27, wherein the releasablelocking mechanism comprises cooperating snap-in elements attached to theguiding profiles and the displacing webs.
 29. The sail assembly of claim27, wherein the guiding profiles comprise rear ends, the releasablelocking mechanism comprises manually adjustable clamping elements whichare attached to the rear ends of the guiding profiles.
 30. A sailassembly, comprising: a mast, a sail comprising two plies, a foldedfront edge, two rear edges and a clew, the sail defining a pocketbetween the two plies, the front edge of the sail being connected to themast, the clew of the sail being connected to a boom, the boom beingbifurcated and extending along each ply of the sail, the boom beingconnected to the mast, the sail defining a sail plane having a totalarea, the rear edges of the sail being connected to at least oneadjustable sail part which is adjustable in the sail plane by adjustingthe lateral position of the adjustable sail part in a first adjustingdirection towards the mast wherein the adjustable sail part moves intothe pocket defined by the sail and the area of the sail plane isdecreased, and by adjusting the lateral position of the adjustable sailpart in a second adjusting direction away from the mast wherein theadjustable sail part is retracted from the pocket and the area of thesail plane is increased, the plies of the sail further comprising aplurality of guiding profiles disposed parallel to each other and theadjusting directions and which extend along inside surfaces of the pliesof the sail, the adjustable sail part comprising a plurality ofdisplacing webs disposed parallel to each other and on opposing surfacesof the adjustable sail part, the guiding profiles serving as sail laths,each displacing web being accommodated in one guiding profile of eachply.
 31. The sail assembly of claim 30, wherein the boom comprises atleast one extendable rear end for increasing a length of the boom alongthe second adjusting direction.
 32. The sail assembly of claim 30,wherein the sail further comprises an upper end area, the upper end areaof the sail comprising at least one sail lath, the plurality of guidingprofiles further comprising two uppermost guiding profiles, oneuppermost guiding profile disposed on each ply, both of the uppermostguiding profiles being disposed below the sail lath of the upper endarea and below the upper end area, the adjustable sail part extendingupwards to the uppermost guiding profiles but below the sail lath of theupper end area.
 33. The sail assembly of claim 30, wherein each guidingprofile accommodates two displacing webs, each guiding profile comprisescross beam disposed between two opposing end sections, the cross beambeing disposed generally perpendicular to the sail plane and to the endsections, the end sections being bent towards each other and forming twoprofiled longitudinal slots with the cross beam disposed therebetween,each profiled longitudinal slot accommodating one of the displacing websof the adjustable sail part.
 34. The sail assembly of claim 33, whereinthe adjustable sail part comprises a rear edge, and the displacing websof the adjustable sail parts are arranged in pairs, each part ofdisplacing webs being accommodated in one of the guiding profiles onopposing sides of the cross beam, each pair of displacing webs beingconnected to one another at the rear edge of the adjustable sail part.35. The sail assembly of claim 30, wherein the guiding profiles comprisea T-shaped cross section with a cross beam that extends perpendicular tothe sail plane, the cross beam of each guiding profile being disposedbetween one of the sail plies and an end section that extends parallelto the sail plane, and the displacing webs comprising two opposingC-shaped cross sections, the end section of each guiding profile beingslidably captured in one of the C-shaped cross sections of one of thedisplacing webs.
 36. The sail assembly of claim 30, wherein theadjustable sail part may be locked into an inward position and anoutward position by a releasable locking mechanism.